Aluminum products, such as, e.g., heat exchangers, machine components, etc., include a large number of components made of aluminum material (including aluminum and aluminum alloys, likewise hereinbelow). These components are often brazed using a brazing sheet that includes a core and a filler metal provided on at least one side of the core. Flux brazing methods, in which brazing is performed by applying flux to a surface of a join part, are widely used as brazing methods for aluminum materials.
In flux brazing methods, a flux that functions to break up oxide films on the surface of the aluminum material is applied to the join part in advance. Then, brazing is carried out by heating the object to be processed in an inert gas atmosphere, such as nitrogen gas or the like. Fluoride-based fluxes containing KF (potassium fluoride), AlF3 (aluminum fluoride), CsF (cesium fluoride), LiF (lithium fluoride), etc. are used as the flux.
However, in flux brazing methods, flux and flux residue remain adhered to the surface(s) of the aluminum products after brazing has been completed. This flux and flux residue sometimes cause problems depending on the usage of the aluminum products. For example, in heat exchangers having electronic parts mounted thereon, there is a risk that problems will occur, such as deterioration of surface treatability during manufacture owing to the flux residue. Further, there is a risk that problems will arise during usage of the heat exchanger, such as clogging caused by the flux, etc., in the refrigerant passageways. Moreover, it is necessary to perform a pickling treatment in order to remove flux and flux residue; in recent years, the cost burden of this processing has been regarded as a problem.
Accordingly, in order to avoid the above-mentioned problems associated with the usage of flux, so-called fluxless brazing methods have been proposed, in which brazing is performed without applying flux onto the surface(s) of the join part(s). Brazing sheets having a filler metal containing Mg (for example, Patent Document 1) are used in fluxless brazing methods. Mg forms a spinel-type oxide (MgAl2O4) on the surface of the brazing sheet during the brazing heating. Brazing can be performed without using flux owing to this oxide embrittling the oxide film present on the join part(s).